Linear data storage media refers to data storage media, such as magnetic tape, in which data is stored in parallel tracks that extend linearly along the length of the media. Examples of linear data storage media include magnetic tape, magneto-optic tape, optical tape, holographic tape, and possibly other tape-like media formats. Magnetic tape media remains an economical medium for storing large amounts of data. For example, magnetic tape cartridges or large spools of magnetic tape are often used to back up large amounts of data for large computing centers. Magnetic tape cartridges also find application in the backup of data stored on smaller computers such as workstations, desktop or laptop computers.
In magnetic tape, data is typically stored as magnetic signals that are magnetically recorded on the medium surface. The data stored on the magnetic tape is often organized along data tracks, and read/write heads are positioned relative to the data tracks to write data to the tracks or to read data from the tracks. As the number of data tracks increases, the data storage capacity of the magnetic tape likewise increases. However, as the number of data tracks increases, the tracks become narrower and more crowded on the surface of the data storage tape. Servo marks are also commonly defined on magnetic media to provide reference points for tracking the location of data tracks. Servo marks can improve the ability to locate data tracks, particularly as the data tracks become narrower and more crowded on the surface of the data storage tape. Servo marks may be recorded in special servo tracks, or interspersed in the data tracks.
Some linear data storage media are “direction-dependent.” Direction-dependent linear media refers to media in which the ability to record data on the media varies based on the direction that the media is moving relative to the recording head. An example of direction-dependent media is metal-evaporated (ME) magnetic tape. In ME tape, the easy axis of magnetic recording domains does not lie in the plane of the tape, but is canted vertically from the plane of the tape. Due to this difference in magnetic geometry, the error rate in the two recording directions at a constant data recording density is typically very different.